The invention relates to a method for operating a storage catalytic converter of an internal combustion engine, especially of a motor vehicle, wherein the catalytic converter is loaded with and unloaded of nitrogen oxides and wherein the storage capability of the storage catalytic converter is reduced because of sulphur contained in the fuel used. Likewise, the invention relates to a control apparatus for an internal combustion engine, especially of a motor vehicle, as well as an internal combustion engine especially for a motor vehicle.
A method of this kind, a control apparatus of this kind and an internal combustion engine of this kind are, for example, known for a so-called gasoline direct injection. There, the fuel is injected into the combustion chamber of the engine in a homogeneous operation during the induction phase or in a stratified operation during the compression phase. The homogeneous operation is preferably provided for the full-load operation of the engine while the stratified operation is suitable for the idle and part-load operation. In such a direct injecting internal combustion engine, a switchover is made between the mentioned operating modes, for example, in dependence upon the requested torque.
It is especially necessary that a storage catalytic converter be present for carrying out stratified operation. With the storage catalytic converter, developing nitrogen oxides can be intermediately stored in order to reduce the same in a three-way catalytic converter during a subsequent homogeneous operation. This storage catalytic converter is loaded with the nitrogen oxides in the stratified operation and is again unloaded in the homogeneous operation. This loading and unloading leads to a deterioration of the storage catalytic converter caused by sulphur and therefore leads to a reduction of the storage capability thereof. The deterioration caused by sulphur is based on the sulphur content of the fuel with which the engine is operated.
It is an object of the invention to provide a method for operating a storage catalytic converter of an internal combustion engine wherein the deterioration of the storage catalytic converter caused by sulphur can be better considered.
This object is solved with the method of the invention of the kind initially mentioned herein in that several states of deterioration of the storage catalytic converter are determined and that a sulphur content of the fuel used is determined from the states of deterioration which follow one another. The object is correspondingly solved with a control apparatus and an internal combustion engine, each of which are of the kind referred to initially herein.
With the invention, the possibility is provided to determine the sulphur content of the fuel used without the use of a special sensor. This presents a significant cost savings. The determined sulphur content can then be used further by the control apparatus in the control (open loop and/or closed loop) of the engine. An improvement of the operation of the engine overall results therefrom.
It is especially advantageous when an ascending slope of the sequential deterioration states is determined and when the sulphur content is determined in dependence upon this slope. This defines an especially simple and therefore rapid way as to how the invention can be carried out.
In an advantageous embodiment of the invention, a specific sulphur content for a specific fuel is determined from a fuel consumption between two regenerations and from a sulphur discharge during a regeneration. In this way, a sulphur content is determined which can be set into relationship with a corresponding ascending slope of the sequential states of deterioration. From this relationship, a conclusion can be drawn from other ascending slopes as to corresponding other sulphur contents.
In an advantageous embodiment of the invention, the time point of a sulphur regeneration is determined in dependence upon the sulphur content. In this way, a very precise control (open loop and/or closed loop) of the engine can be achieved especially with a view toward the least possible exhaust-gas emissions.
In a further advantageous embodiment of the invention, the intensity of a regeneration is determined in dependence upon the sulphur content. Here also, an improvement of the control (open loop and/or closed loop) of the engine with a view to the exhaust-gas emissions and the fuel consumption is obtained.
Of special significance is the realization of the method of the invention in the form of a control element which is provided for a control apparatus of an internal combustion engine, especially of a motor vehicle. A program is stored on the control element which can be run on a computing apparatus, especially on a microprocessor, and is suitable for executing the method in accordance with the invention. In this case, the invention is therefore realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same way as the method for whose execution the program is suitable. As a control element, an electric storage medium is especially applicable, for example, a read-only-memory or a flash memory.